Earlier this year, an Indian court convicted Aditi Sharma of murdering her fiancé. Although she maintains her innocence, Sharma was convicted based on a brain electrical oscillation signatures test, which the prosecution claimed proved that she possessed experiential knowledge of the crime. Now some individuals are looking to introduce brain scan evidence in US courts as well. Could your brain waves really be used to convict you of a crime? We give you the legal breakdown.In the US, scientific evidence presented during a trial must meet the Daubert standard (or, in some jurisdictions, the Frye standard). To be admissible, an expert’s scientific testimony must be relevant to the case, and the expert must have arrived at his or her conclusions through the scientific method. If the admissibility of the evidence is challenged, a judge will consider the use of empirical testing, whether the expert’s method of drawing conclusions has been subject to peer review, whether the error rate of such conclusions is known so that it may be disclosed during trial, and whether the method and conclusions have been accepted by a significant proportion of the scientific community. Currently, brain scans can be entered into evidence, but they are generally used by defendants to mitigate culpability. Scans can show that a defendant suffers from brain damage, a tumor, or a neurological defect that impairs their judgment, perception, ability to control their actions, or sense of right and wrong. In the 2005 case Roper v. Simmons, which famously held that it is unconstitutional to execute individuals for crimes they committed as a minor, the Supreme Court admitted fMRI readings into evidence of the biological differences between adolescent and adult brains. This indicates that the court system does put stock in these tests under certain circumstance. But, for courts to start admitting brain scans as evidence of criminal activity, they would have to pass the Daubert standard. Unfortunately for defendants, some legal scholars have deemed Daubert “near irrelevant,” as certain judges err on the side of including too much evidence, and defendants are unlikely to win Daubert challenges against the prosecution. And this can prove problematic when the evidence is presented to CSI-loving jurors who are more likely than judges to view scientific testimony as infallible. But even if courts accept the scientific methodology behind this use of brain scans, there are still constitutional issues to consider. The Fifth Amendment of the US Constitution states that no person “shall be compelled in any criminal case to be a witness against himself.” And courts will have to determine whether the use of brain scans by the prosecution presents an unlawful compulsion of testimony from the defendant. A defendant’s physical body can be used as evidence against him in certain circumstances. For example, the state can compel a criminal suspect to provide a DNA sample, and can even take blood from an unconscious suspect to determine whether there are drugs or alcohol in the defendant’s system and later enter the results into evidence. But unlike brain scans, these are not communicative acts and they do not reveal the content of the mind. The closest analogy we have to brain scan lie detectors is the polygraph. Like brain scans, polygraphs purport to offer a glimpse into a suspect’s mind. Although the Supreme Court has never ruled on the introduction of a defendant’s polygraph by a prosecutor, it alluded to the problem of polygraphs in Schmerber v. California. The case, which upheld the admissibility of a blood test taken without a defendant’s consent, distinguished taking this type of evidence from measuring physiological responses”

Some tests seemingly directed to obtain "physical evidence," for example, lie detector tests measuring changes in body function during interrogation, may actually be directed to eliciting responses which are essentially testimonial. To compel a person to submit to testing in which an effort will be made to determine his guilt or innocence on the basis of physiological responses, whether willed or not, is to evoke the spirit and history of the Fifth Amendment. Such situations call to mind the principle that the protection of the privilege "is as broad as the mischief against which it seeks to guard." Counselman v. Hitchcock, 142 U. S. 547, 142 U. S. 562.

However, polygraphs have been successfully introduced by prosecutors during sentencing proceedings. In the 2006 case United States v. Johnson, the 2nd Circuit upheld the introduction of Jeffrey Johnson’s polygraph results, whose introduction he had stipulated to prior to taking the test, stating that it did not violate his Fifth Amendment rights. And even if brain scan evidence is never successfully introduced in court, it could still be used the same way polygraphs are today: to coerce suspects who fail the tests into making a confession. Complex brain imaging is making waves in court [SF Gate]